In the field of containers for foods and beverages, laminated metal sheets which are formed by laminating a resin film to a metal sheet have been used in place of the conventional plated steel sheets and coated aluminum sheets. So far, methods for manufacturing these laminated metal sheets have been known (Japanese Patent Laid-open Publication No. Hei-4-201237, for example). They are excellent in the respect that they use no solvent and no ovens for baking finish, differently from the case of manufacturing coated metal cans.
The laminated metal sheets for containers use should satisfy various requirements, for example, good adhesion of a film to a metal sheet endurable to press-forming, deep drawing, ironing, or the like when they are formed into cans and no disfigurement of the surfaces thereof so that the resin film can be free from damages during forming. In this regard, therefore, generation of bubbles in the laminated metal sheet is undesirable because the adhesion between the resin film and the metal sheet is decreased, the surface of the laminated metal sheet is roughened, which easily causes the surface to suffer damages during forming, and further the appearance of the laminated metal sheet is degraded, all due to the bubbles. Therefore, efforts have been made toward preventing the generation of bubbles in the laminated metal sheet when it is manufactured.
Today, as the demand for the laminated metal sheets increases, it is more required to increase lamination speed for the purpose of improving the productivity thereof. However, when the lamination speed is simply increased, a great quantity of bubbles generate, which is the reason why the lamination speed is so far limited.